The present invention relates to devices and methods for testing photodiodes, and, more particularly, to noncontact, nondestructive test devices and methods for photodiode detector arrays or mosaics.
Currently, the performance of two dimensional arrays of photodiode detectors may be tested by a variety of techniques, both contact and noncontact. The most common test procedure involves mechanically connecting (i.e., "bumping") the detector mosaic to a charge coupled device ("CCD") from which traditional performance measures, such as the zero voltage device resistance ("r.sub.o ") of the device, may be easily derived. However, this process is time-consuming and wasteful, especially if the detector performance is substandard. In such case, the detector mosaic is discarded, including the CCD which cannot be easily disconnected from the device.
Detector arrays or mosaics may also be characterized by mechanical probes which are moved sequentially across the mosaic, measuring the r.sub.o at each detector. Where large arrays are tested this approach can be extremely time-consuming. This process also requires metalization of the detector substrate and physical contact with that metalization. Thus, the detector may be physically damaged by the probe or possible inaccurate measurements may result due to electrical loading from the probe.
Electron beam ("e-beam") test devices which provide noncontact testing, nevertheless present similar problems. In e-beam testing, a known charge imparted by the e-beam is used to reverse bias each detector. The time required for this charge to dissipate is measured, from which, in combination with the amount of charge and other known parameters, the device quality may be calculated. One disadvantage of the e-beam technique is that it requires that gold contacts be formed over the N.sup.+ region of each photodiode to serve as a surface for e-beam illumination. This additional processing step is both expensive and time consuming. A second disadvantage of this technique is that a precise mask must be positioned over the detector array so that the e-beam will not strike the P substrate of the photodiode, which would destroy the device.
It is, accordingly, an object of the present invention to provide a completely noncontact, nondestructive device and method for testing photodiode detector arrays or mosaics which requires no special sample preparation of any kind, and which may be fully automated.